The present invention is directed to a formulation for a black conversion coating and in particular to a conversion coating which provides a consistent and adherent black finish on nickel and nickel-plated substrates.
Black conversion coatings are applied to various substrates. Often, the coating is a black non-electrolytic conversion coating which is applied to nickel and nickel-plated substrates. One known formula has been used for many years which formula did not perform satisfactorily in production situations. The known formula is a liquid concentrate to which three parts by volume of water is added to one part of the liquid concentrate. The formulation is used at a temperature of 180.degree. F.
The known coating formulation produces an inconsistent black finish on nickel and nickel-plated substrates and both the concentrate and the working solution have very minimal shelf life. The liquid concentrate is formulated from sodium thiosulfate and cobalt sulfate, each of which comprises, respectively, 175 grams and 100 grams per liter of water.